1. Field of the Invention
The present invention relates to an echo canceller and a microphone apparatus and, more particularly, to an echo canceller that executes adaptive processing for canceling an echo component from an audio input signal and a microphone apparatus having this echo canceller.
2. Description of the Related Art
As typified by a television conference system, conference systems are known in which audio and video signals data are transmitted and received between remotely arranged terminals for remote conferencing. A microphone apparatus (hereafter simply a microphone) for use in conference systems has an audio processing block for processing an audio input signal picked by the microphone. In the audio processing block, an incorporated echo canceller executes processing on an audio input signal picked up by the microphone of a conference system for canceling an echo caused by the reflection of a sound outputted from the speaker of the conference system into the microphone thereof.
The echo canceller such as mentioned above learns the echo component contained in each audio input signal and executes an adaptive operation by use of an adaptive filter, for example, thereby stabilizing the echo cancel processing. In a single-talk state where a single speaker is making a talk, an adaptive operation normally function. However, in a double-talk state where two or more speakers are making a talk, including the first speaker, the audio signals generated by other speakers get mixed, thereby causing the adaptive operation not to function normally. Therefore, executing adaptive processing in the double-talk state cancels not only the echo component but also the voice component of the speakers. To minimize this adverse effect, the echo canceller makes a distinction between single-talk and double-talk and, in the case of double-talk, does not executes the learning for adaptive processing.
One of the methods for making a distinction between single-talk and double-talk is the Geigel algorithm. In this algorithm, a ratio between the volume of an audio signal outputted from a loudspeaker and the volume of an audio signal picked up and inputted by a microphone is computed. If the obtained ratio is less than a predetermined fixed value, it is determined to be single-talk; otherwise, it is determined to be double-talk.
Some echo cancellers monitor a path along which an audio signal inputted from the microphone travels and a path along which an audio signal to be outputted to the loudspeaker travels and, if the audio signals traveling along both the paths continue sounded for more than a predetermined period of time, it is determined to be double-talk (refer to Japanese Patent No. 3579245 (Paragraphs [0047] through [0062], FIG. 6) for example).